NMR spectroscopy is an efficient method of instrumental analysis. In this process, RF pulses are radiated into a test sample, which is located in a strong, static magnetic field, and the RF reaction of the test sample is measured. Thereafter, the information is obtained integrally over a certain region of the test sample, known as the active volume. The test sample generally consists of a cylindrical sample tube, which contains the measurement substance to be examined in solid or liquid form. The sample tube is typically located in a spinner. The sample tube and spinner are transported from outside the magnet into the NMR probe using a transport system. When the sample tube is in the measurement position, the spinner is inside the turbine. The turbine allows the sample tube to rotate. In the measurement position, the sample tube is surrounded by one or more NMR coils. The innermost NMR coil has an inside diameter that is larger than the outside diameter of the measurement probe by as little as possible, since the space factor and thus the sensitivity of the NMR probe depends on the inside diameter and decreases as the inside diameter increases.
The temperature of the sample inherently influences the results of the NMR measurements. For high-quality measurements, the temperature is typically set using a temperature-control unit and is kept as spatially and temporally constant as possible over the active measurement volume. NMR measurements are typically carried out using both heated and cooled samples. (If the sample is intended to be cooled to below room temperature, a sufficiently cool temperature-control fluid flow is carried in the inflow pipe and heated to the desired temperature by the heater.) The spatial temperature gradient over the active measurement volume and the stability over time of the sample temperature have a significant impact on the quality of the NMR measurements. DE10 2010 029 080 A1 and DE 40 18 734 C2 disclose temperature-control units for minimizing the temperature gradients in the active measurement volume.
EP 1 655 616 A1 or US 2006/0096301 A1, for example, describe NMR equipment comprising an NMR cryogenic probe cooled to an operating temperature of <100 K and comprising a cooling circuit having thermally insulated cooling lines between the heat-insulated housing and the NMR cryogenic probe.